The following points highlight the five classes of the phylum platyhelminthes. The classes are: 1. Turbellaria 2. Monogenea 3. Dlgenea (Flukes) 4. Aspidagastrea 5. Cestoda (Tape worm).
Class # 1. Turbellaria:
1. Mostly free-living non-segmented worms, anterior end often bears eyes and a triangular projection.
2. The ectoderm is ciliated, often glandular and with peculiar rod-like bodies.
3. A pair of anteriorly placed ganglia give off lateral nerve cords.
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4. Digestive cavity always blind with a protrusible, often branched muscular pharynx.
5. Excretory pores variable in number and position—either single posterior pore, or a pair of lateral pores, or numerous scattered pores or excretory system absent.
6. Some forms multiply by fission; regeneration also occurs.
7. Life cycle usually direct with juvenile worm, emerging from egg or cocoon.
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8. Marine, fresh water and some terrestrial.
9. Size varies from microscopic to ones more than 60 cm. in length (land planarians), but most are less than 10 mm long. Examples: Convoluia, Temnocephala, Bipalium, Planaria, Dugeiia, Nematoplana, etc.
Class # 2. Monogenea:
1. Typically ectoparasites of the skin and gills of fishes but some have become endoparasitic in the coelom and very rarely in the gut of fishes, others in the pharynx and urinary bladder of amphibians and reptiles.
2. Epidermis of adult devoid of cilia and rhabdites.
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3. Gut really always present (except in Gyrocotylidea) and typically with pharynx and bifurcated intestine, with mouth either simple or surrounded by an oral sucker.
4. Main attachment organ (the haptor) always posterior and terminal, typically armed.
5. Excretory system terminating in a pair of lateral pores at the anterior end.
6. Free-swimming larva provided with 10-16 posterior marginal hooks and, sometimes, one or two pairs of median hooks in addition.
7. Life cycle simple, no larval multiplication, confined to a single host (usually vertebrate).
Examples: Entobdella, Gyrodactylus, Potystoma, Gyrocotyle (endoparasite in intestine of holocephalan fishes), etc.
Class # 3. Dlgenea (Flukes):
1. Body leaf-like or cylindrical; endoparasites with epidermis devoid of cilia in the adult.
2. Gut always present, provided typically with oral sucker, pharynx and bifurcate intestine.
3. A simple, unarmed ace tabulate ventral sucker present as attachment organ.
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4. Excretory system in adult terminates in a single posterior pore.
5. The life cycle complex involving more than one host; a free-swimming larva enters a gastropod or lamellibranch and multiply by polyembryony and develop free-swimming tailed cercaria larva which enters another host to form metacercaria; metacercaria enters the final host to attain adult stage.
Examples: Fasciola, Echinostoma, Cotylophoron, Schistosoma (blood fluke), etc.
Class # 4. Aspidagastrea:
1. Endoparasites; epidermis of adult devoid of cilia and rhabdites.
2. Gut always present, without oral sucker (funnel-like mouth) followed by pharynx and simple intestine.
3. Very large ventral sucker, subdivided into one or more longitudinal rows of alveoli or several distinct suckers.
4. Single pair of posterior excretory pores.
5. Development either direct or two hosts cycle in which the adult, parasite on a mollusc persists in the intestine of a fish or a reptile. Example: Aspidogaster.
Class # 5. Cestoda (Tape worm):
1. Endoparasitic; epidermis of adult devoid of cilia and rhabdites, but with microvilli; body elongated, tape-like.
2. Gut completely absent.
3. Head or scolex usually round and bears blind suckers, hooks, bothria etc.
Subclass i. Cestodaria:
1. Body not divided into proglottids.
2. Only one set of gonad.
3. Ten hooks present in larva. Example: Atnphilina.
Subclass ii. Eucestoda:
1. Body long, ribbon-like, consists of a scolex (head), un-segmented neck, and a number of proglottids.
2. Six hooks are present in larva.
3. Each segment (proglottid) is provided with both sets of reproductive organs.
Examples: Taenia, Diphylobothrium, Tetrahynchus, Echinococcus, etc.